In the manufacture of hybrid circuits, it is frequently necessary or desirable to establish a conductive bond between two metallic members. For example, it may be desired to establish such a bond in order to provide a conductive connection between a layer of metallization that has been deposited by thin-film evaporation techniques on a ceramic substrate to form a conductor run, and a metallic member that constitutes a lead for connecting the conductor run to another circuit element.
It is conventional to use a solder preform in order to provide a conductive bond between a metallic lead and a thin-film conductor run on a ceramic substrate. However, use of a preform is subject to the disadvantage that it requires three components (substrate, lead and preform) to be brought into alignment. Moreover, solders in general are subject to the disadvantage that their low melting points (below about 500 degrees C.) require that subsequent processing of the hybrid circuit be carried out at relatively low temperatures in order to avoid degrading the bond.
In the manufacture of a hybrid circuit, it is conventional to secure a lid to the substrate in order to isolate the monolithic integrated circuit chip mounted on the substrate from the environment in which the hybrid might be used. Generally, the lid is secured to the substrate by soldering. In order to isolate the IC chip effectively, throughholes in the substrate must be sealed, and it has been conventional hitherto to use a filling of glass or plastic material to seal such throughholes. However, at temperatures used for soldering the lid to the substrate some plastics and glasses have a negative temperature coefficient of expansion and consequently tensile stresses may be created in the substrate material. In the case of a ceramic substrate material this may be a disadvantage, because ceramics, although strong in compression, are relatively weak in tension.